1. Field of the Invention
The present invention relates to optical imaging and motion detection. The invention has particular applicability to integrated circuits and firmware used in optical handheld pointing devices, such as a computer mouse.
2. Description of the Related Art
The prior art includes a number of different techniques for estimating and detection motion of an image principally by comparing successive images in time to detect motion. These include:
U.S. Pat. No. 6,859,199 incorporated by reference herein, works primarily through feature extraction. The disclosed algorithm works by:                Extracting a first feature set from a first image and a second feature set from a second image subsequent in time to the first image;        Comparing the first feature set to the second feature set to determine a shift in position of the second image relative to the first image;        Outputting a motion vector based upon the shift in position.        
The drawbacks of this technique include the fact that there must be a fairly large number of elements in the first and the second feature sets to determine the motion vector accurately.
U.S. Pat. No. 5,729,008 and U.S. Pat. No. 5,786,804 both also incorporated by reference herein, disclose a form of block matching which operates as follows:                Capturing a first frame and a second frame;        Correlating the signals of the first frame to the signals of the second frame;        Generating a correlation output of the motion.        
The drawback of this approach is that, when using only one block to perform block-matching method, the elements in this block must be sufficient to ensure accuracy of matching. Moreover the larger this block gets, the more complicated a computation and memory also becomes.